When using the Markup feature in Field Maps to leave notes, how do you share the original data that they making notes about when sharing the mark up layer to ArcOnline?
Example: Field worker goes to field and draws a circle over points that need to be reviewed and makes notes in that mark up that are specific to those exact points in the field. He then shares the markup and the notes are there but the data he collected over notes over is not and we do not know what he was referencing
Most data collection workflows will involve feature layers with editing enabled. Markup is a simple method intended to capture sketches and notes on a local device. The original data capture app ArcGIS Collector did not have Markup, but the free/cheap version Explorer did, and this came to Field Maps with the merger of all map-centric apps.
The markup is not associated with your map. It can be shared. Most practically it will be shared as an image, similar to adding notes to a pdf exported from Pro. You can share the raw markup data, but there are some limitations. You can open the markup on another Field Map or have a Creator publish it as a markup item and then add it to a map, access it in Pro etc. But again users would have to find and add it to the map.
So in your case, you can add the Markup to a Field Map and open it on top of the map. Or you can upload it to ArcGIS Online (Creator/Pro licence) and add it to the same map as a markup item in the Web Map or ArcGIS Pro.
Long term, if you have users intending to make notes or capture data in the field, I would recommend setting up the device for that purpose - i.e. using a licence + Hosted Feature Layers. Mark-up is otherwise fine, but it will be a bit more limited for its purpose.